DNA tests by University of Tennessee
researcher Sunitha Vege pinpointed corn ear
worm and tobacco budworm moths in bats'
feces. While nursing hungry pups (right),
female freetails need to eat up to 70 percent
of their weight in insects nightly.
or so, calculations show that a million bats can
devour about ten tons of insects nightly. That
means the 100 million free-tailed bats in
south-central Texas must eat an incredible
1,000 tons-two million pounds-of insects in
a single night.
Since bats in other locales pursue insects
close to the ground, we wondered why the free
tails were flying as high as 10,000 feet. Is this
where they find the billions of insects needed
to sustain their huge populations?
Again, Doppler radar offered clues by detect
ing the billions of insects that swarm high
above Texas. Since the 1980s researchers from
the United States Department of Agriculture
have used radar to map the flight patterns of
some of North America's most destructive
agricultural pests-fall armyworms, beet army
worms, tobacco budworms, and, the worst of
all, corn earworms.
Corn earworms and tobacco budworms
alone cost U.S. farmers over a billion dollars
annually. To control them, Texas cotton grow
ers spread nearly 30 million dollars' worth of
insecticides between 1995 and 1997 but still
lost an annual average of 148,000 bales of
cotton (each worth $350).
"Some years we've had to spray three to
five times at a cost of $30 to $50 an acre,"
says Ray King, a farmer in the Winter Garden.
"I'll never forget June of 1995 when the beet
120
armyworms ate our lunch. We'd have been
better off if we'd just let them have the crop."
During the first weeks of June each year
about the time the bats give birth-up to seven
billion corn earworm moths, plus a similar
number of fall armyworm moths and other
pests, emerge from the cornfields of the lower
Rio Grande Valley. After dusk they ascend any
where from hundreds to thousands of feet and
ride the prevailing winds north to the Winter
Garden. They can make the 250-mile flight in
one night. Each female then lays as many as a
thousand eggs in corn, cotton, and other crops,
where the larvae grow fat as they mature.
Texas farmers are only the first in the United
NATIONAL GEOGRAPHIC, APRIL 2002